ACOUSTICS

The science of how sound behaves, especially when it
travels through our everyday world, is called acoustics. Sound waves normally
travel in straight lines directly outwards from their source, but they do not
always travel in that way. An object standing in the path of a sound wave can
affect its movement. When a sound wave hits a hard object, the sound reflects
back towards the source in the form of an ECHO. When soft objects
get in the way, they can ABSORB the sound and stop it from
travelling any further. Scientists use sound reflection and absorption to
investigate places that they cannot visit, such as the depths of oceans and the
interior of the Earth.

HOLLYWOOD BOWL

The Hollywood Bowl is a famous, open-air amphitheatre in California,
USA. An amphitheatre is a bowl-shaped place that reflects sound naturally and
evenly into the landscape around it. The Hollywood Bowl was carved into the
side of a mountain at Bolton Canyon in the 1920s and can seat 20,000
people.

CONCERT HALL

Music must sound clear in an auditorium, no matter where people are
sitting in the audience. It should sound the same whether the hall is full or
nearly empty. The curved shapes in modern concert halls are designed to help
distribute the sound evenly to every seat in the auditorium.

ECHOES

If you shout at a distant wall, you can hear your voice
return as a reflected sound wave, or echo. When the reflected sound wave has to
travel some distance, it takes time to return and you hear it separately from
the original sound. Sound waves that reflect off nearer objects return almost
instantly. Our brains blend these waves with the original sound and we hear no
echo.

ECHOLOCATION

Like many other sea creatures, dolphins use sound to find their
way around, locate their companions, and discover sources of food. The clicking
sounds they make are reflected back from the seabed and objects around them and
are picked up by the dolphins’ long, bony heads. Using echoes to find
things is known as echolocation.

EXPLORING WITH SONAR

The depth of the ocean can be measured using SONAR (SOund
Navigation And Ranging). A loudspeaker under the ship sends down a beam of
high-frequency ultrasound. Echoes of the sound waves are detected by hydrophone
(underwater microphone) as they bounce back up.

ABSORPTION

Hard objects reflect sounds, but soft materials absorb
sounds and silence them. When sound waves reach a soft material, their energy
is soaked up and they travel no further. Things that absorb sound can be useful
for reducing noise. Trees are sometimes planted by motorways so that their
leaves will reduce the sound of traffic. Walls can be padded with soft
materials to stop sound from travelling through them.

ANECHOIC CHAMBER

Engineers test loudspeakers and audio equipment in specially
designed laboratories called anechoic chambers. The walls and ceiling are
covered by spikes of soft foam that absorb sound and stop any echoes and
reverberations (very fast echoes). Sounds made inside an anechoic chamber sound
very dull or “dead”, which is why the chambers are also called
“dead rooms”.